The present invention relates to an image recording sheet and a material for forming a covering layer of the image recording sheet and, more particularly, to an image recording sheet for recording of a predetermined image by image recording apparatus of the ink jet method etc., and a material for forming a covering layer of the image recording sheet.
In general, many image recording sheets are used for recording the predetermined image, for example, by the image recording apparatus of the ink jet method and the other methods.
On the conventional image recording sheets of this type, in order to record a high-quality image on the sheet surface from an original picture of high resolution, there were demands for formation of an ink receiving layer capable of preventing diffusion of ink having a property of diffusing on the sheet surface and thus forming a digital-look image.
For meeting the demands, it was conventional practice to form the ink receiving layer of a predetermined thickness whose principal components are boehmite having an average particle size of not more than 0.1 xcexcm and alumina microparticles, on a surface of a base material.
In order to protect the ink image recorded in the ink receiving layer, it was also conventional practice to cover the surface of the ink receiving layer by a covering layer made of an appropriate covering material.
The conventional image recording sheets described above, however, had the following disadvantages.
Namely, the conventional methods for forming the covering layer over the ink receiving layer normally involved coating the ink receiving layer with the covering layer and thereafter drying it, thereby completing the covering layer, and thus had the problems of long time necessary for the formation of the covering layer, and high cost.
Since the average particle size of boehmite was very small, the base material was coated with a sol form of boehmite synthesized with an appropriate binder; during the coating there occurred such incidents that the ink receiving layer cracked and that the image recording shoot itself curled, which made use thereof in image recording impossible. In order to stabilize the coating layer of boehmite on the surface of the base material, the coating layer also needed to be preliminarily baked at about 150xc2x0 C., and the heating resulted in leaving unevenness of the image recording sheet itself, so as to make use thereof in image recording impossible. The coating layer of boehmite absorbed cigarette smoke etc. to yellow, so as to become unapplicable to image recording. Further, the coating layer of boehmite absorbed the ink well to prevent diffusion of the ink and be able to form the digital-look image; on the other hand, the ink remained in units of sizes of ink dots, so that it failed to record an analog-look image, i.e., an image like a silver-salt photograph.
The present invention has been accomplished in view of these aspects and overcame the aforementioned problems of prior art, and an object of the present invention is to provide an image recording sheet and a material for forming a covering layer of the image recording sheet by which the covering layer can be formed easily and at low cost on the image reception layer, by which the covering layer can be made to firmly cover the ink receiving layer, in which there occurs none of damage such as peeling of the covering layer off the ink receiving layer or the like, by which it is possible to record a high-quality and analog-look image, i.e., an image like a silver-salt photograph, by which the gloss can be adjusted, and which are excellent in water resistance, weather resistance, and so on, easy in production, and low in cost.
In order to accomplish the above object, the inventors conducted intensive and extensive research and found out the following, so as to accomplish the present invention; in cases where the covering layer is formed by transferring it onto the ink receiving layer and where a material of the covering layer and a material of the ink receiving layer are congenial to each other, if the covering layer is formed by transferring the covering layer formed on a release sheet onto the surface of the ink receiving layer, the covering layer can be made to cover the ink receiving layer easily and firmly, without occurrence of the damage such as peeling of the covering layer off the ink receiving layer or the like; in cases where a transfer auxiliary layer made of a material different from the two layers and congenial to them is preliminarily formed to cover at least one of them and where the covering layer is transferred onto the surface of the ink receiving layer with the transfer auxiliary layer in between, the covering layer can be made to cover the ink receiving layer easily and firmly, as above, without occurrence of the damage such as peeling of the covering layer off the ink receiving layer or the like; in cases where the same material as that for forming the covering layer is preliminarily formed as a thin layer on the surface of the ink receiving layer, irrespective of the congeniality of the two layers and where the covering layer formed on the release sheet is transferred thereonto, the covering layer can be made to cover the ink receiving layer easily and firmly, without occurrence of the damage such as peeling of the covering layer off the ink receiving layer or the like. Further, the inventors also found out the following, so as to complete the present invention; an excellent image recording sheet can be obtained by using a swelling resin and a solid component as components of the ink receiving layer and adjusting a mixture rate of the two components, and the maximum size and average grain size of the solid component.
Namely, an image recording sheet according to the present invention is an image recording sheet used for recording an image in an ink receiving layer formed on a surface of a base material by an image recording device of an ink jet method or the like and covering surfaces of the ink receiving layer and the image by a covering layer to record a predetermined image, wherein said covering layer is formed by transferring a covering layer, which is formed in a separable state on a release sheet, onto said ink receiving layer. Since in the image recording sheet formed as described above the material of the ink receiving layer and the material of the covering layer are congenial to each other, the covering layer formed in the separable state on the transfer sheet of the covering-layer-forming material to the ink receiving layer can be transferred directly onto the surface of the ink receiving layer, whereby the ink receiving layer and the directly transferred covering layer congenial to each other can adhere to each other with large adhesive strength.
Another image recording sheet according to the present invention is an image recording sheet used for recording an image in an ink receiving layer formed on a surface of a base material by an image recording device of an ink jet method or the like and covering surfaces of the ink receiving layer and the image by a covering layer to record a predetermined image, wherein a transfer auxiliary layer is preliminarily provided to cover at least one of a surface of a covering layer, which is formed in the separable state on a release sheet, and the surface of said ink receiving layer and the covering layer is formed by transferring said covering layer onto said ink receiving layer with said transfer assist layer in between. With the image recording sheet formed as described above, the covering layer can be transferred onto the surface of the ink receiving layer with interposition of the transfer auxiliary layer made of the material different from the material of the ink receiving layer and the material of the covering layer and congenial to the both and preliminarily formed to cover at least one of the both. This permits the covering layer to cover the ink receiving layer easily and firmly with the transfer auxiliary layer in between and nullifies occurrence of the damage such as peeling of the covering layer off the ink receiving layer or the like. As a consequence, the ink receiving layer can be protected well even if the whole covering layer is formed in small thickness. In this way, according to Claim 2, the ink receiving layer and the covering layer both can adhere to each other firmly, irrespective of the congeniality between the material of the ink receiving layer and the material of the covering layer. Accordingly, this is extremely effective when applied to a combination of such materials that the covering layer transferred is readily peeled off the ink receiving layer because of poor congeniality of them.
Another image recording sheet according to the present invention is an image recording sheet used for recording an image in an ink receiving layer formed on a surface of a base material by an image recording device of an ink jet method or the like and covering surfaces of the ink receiving layer and the image by a covering layer to record a predetermined image, wherein said covering layer is formed by preliminarily forming a thin preformed covering layer of the same material as the covering layer, on the surface of said ink receiving layer and transferring a covering layer, which is formed in a separable state on a release sheet, onto said preformed covering layer. With the image recording sheet formed as described above, since the preformed covering layer made of the same material as the covering layer is preliminarily formed as a thin layer on the surface of the ink receiving layer of the image recording sheet, the covering layer formed in the separable state on the transfer sheet of the covering-layer-forming material can be transferred onto the preformed covering layer formed on the ink receiving layer so as to cover it. This permits the transferred covering layer to be firmly integrated with the preformed covering layer on the ink receiving layer and thus increases the adhesive strength of the whole covering layer to the ink receiving layer, whereby the covering layer can be made to cover the ink receiving layer easily and firmly, without occurrence of the damage such as peeling of the covering layer off the ink receiving layer or the like. As a consequence, the ink receiving layer can be protected well even if the whole covering layer is formed in small thickness. In this case, the material of the preformed covering layer can be the same as the material of the covering layer directly transferred onto the preformed covering layer, but the material of the preformed covering layer may be different, for example, from the material of the part of the covering layer not transferred directly onto the preformed covering layer. In this way the present invention permits the ink receiving layer and the covering layer to adhere to each other firmly, irrespective of the congeniality between the material of the ink receiving layer and the material of the covering layer. Accordingly, it is extremely effective when applied to a combination of such materials that the transferred covering layer is peeled readily off the ink receiving layer because of poor congeniality of them.
The image recording sheet according to the present invention is also characterized in that the ink receiving layer has a composition in which 10 to 300 parts by weight, of a solid component are mixed per 100 parts by weight of a swelling resin component, and in that the solid component has a maximum size equal to a half or less of a thickness of the ink receiving layer, and an average grain size of 1 to 10 xcexcm. According to the invention formed as described, the ink can be received properly, where the mixture rate of the solid component to the swelling resin as components of the ink receiving layer is 10 to 300 parts by weight per 100 parts by weight of the swelling resin component; pinholes can be prevented from appearing in the ink receiving layer, where the maximum size of the solid component is a half or less of the thickness of the ink receiving layer; a high-quality and analog-look image, i.e., an image like a silver-salt photograph can be recorded and the gloss thereof can be adjusted, where the average grain size of the solid component is 1 to 10 xcexcm.
The image recording sheet according to the present invention is characterized in that the solid component is silica. The invention formed as described can make the image recording sheet more excellent.
The image recording sheet according to the present invention is also characterized in that the material forming the covering layer is latex. The invention formed as described permits the image formed in the ink receiving layer to be covered by the covering layer of transparent latex, so as to make the image look like a photograph, whereby the quality of the image can be improved greatly.
The covering-layer-forming material of the image recording sheet according to the present invention is one wherein the covering layer is formed in a separable state on a release sheet. According to the present invention formed as described, the covering layer can be stripped away from the release sheet to be transferred onto the surface of the ink receiving layer so as to cover it.
The covering-layer-forming material of the image recording sheet according to the present invention is characterized in that the material forming the covering layer is the latex. According to the invention formed as described, the image formed in the ink receiving layer can be covered by the covering layer of the transparent latex, so as to make the image look like a photograph, whereby the quality of the image can be improved greatly.
Since the image recording sheet and the covering-layer-forming material of the image recording sheet according to the present invention are constituted and act as described above, they have the following effects without occurrence of the problems as encountered in prior art; the covering layer can be formed easily and at low cost on the ink receiving layer, the covering layer can be made to cover the ink receiving layer firmly, they are free of the damage such as peeling of the covering layer off the ink receiving layer or the like, they permit recording of a high-quality and analog-look image, i.e., an image like a silver-salt photograph, they permit adjustment of gloss, they have excellent water resistance, weather resistance, etc., their production as easy, the cost is low, and so on.